1. Field of the Invention
The invention relates to the field of inspection systems and, in particular, to an apparatus for measuring the attenuation of electromagnetic radiation through honeycomb core coated with electromagnetic radiation absorbing materials.
2. Description of Related Art
Honeycomb core is often used in the leading and trailing edges of airfoils and other control surfaces as and numerous other locations on aircraft. In order to achieve a low radar cross-section, the core is coated with radar absorbing materials. However the core must be inspected to insure that it has the required absorbing properties. This is normally accomplished prior to machining to its final shape and, certainly prior to the bonding of cover sheets there over. Otherwise failure to meet the absorption requirements would result in the scrappage of very expensive parts. If the core is inspected immediately after coating, reworking, in most instances, becomes an easy task. In the past, bulk properties were measured be illuminating the coated core and determining the overall absorption thereof. However, this procedure while, easily determining whether a part was acceptable, could not isolate the imperfections in a failed part.
U.S. Pat. Nos. 4,829,238, "Method And Apparatus for Monitoring Electromagnetic Emission Levels" by R. R. Goulette, et. al. and 5,028,866, "Method And AppAratus Form Mapping Printed Circuit Fields" by R. W. Wiese are both interest in that they disclose the use of small antenna probes to monitor and map the emissions from printed circuit boards. However, they are on no use in the inspection of honeycomb core since they depend upon sensing emissions from the object being monitored and honeycomb core is not itself an emitter. U.S. Pat. No. 4,588,993, "Broadband Isotropic Probe System For The Simultaneous Measurement of Complex E- And H-Fields" by T. M Babij, et. al. is of more interest in that it uses a combination of three mutually orthogonal dipole antennas and a set of three mutually orthogonal loop antennas to map the E and H fields of a closed space. However, it does not teach the use of a pair of antennas to transmit and receive electromagnetic radiation within honeycomb core to measure the attenuation of a transmitted signal for determining the acceptability of the core as a radar absorbing structure.
Thus it is a primary object of the subject invention to provide an apparatus for measuring the attenuation of electromagnetic radiation through honeycomb core coated with electromagnetic radiation absorbing materials.
It is another primary object of the subject invention to provide an apparatus for measuring the attenuation of electromagnetic radiation between individual cells of honeycomb core coated with electromagnetic radiation absorbing materials.
It is a further object of the subject invention to provide an apparatus for measuring the attenuation of electromagnetic radiation through honeycomb core coated with electromagnetic radiation absorbing materials at various frequencies.
It is a still further object of the subject invention to provide an apparatus for measuring the attenuation of electromagnetic radiation at various locations within honeycomb core coated with electromagnetic radiation absorbing materials.